1. Field of the Invention
The present invention is directed to a bi-directional pressure sensing probe for measuring fluid flow in a pipe and, more particularly, to a probe that indicates flow direction as well as maximizes the pressure signal produced by the probe and/or minimizes flow disturbance created by the probe.
2. Background of the Invention
In many applications it is important to know not only the magnitude of fluid flow in a pipe but also the direction. Reverse direction flow can sometimes damage very expensive equipment. One such application is a steam generator steam extraction line. Reverse flow in this line can be accompanied by the reverse flow of liquid rather than steam. Reverse water flow in a steam turbine can be very damaging. Monitoring reverse flow conditions in extraction lines is very important. Prior art pressure sensors determine static pressure in fluid pipes by positioning the pressure sensing orifice in the pipe wall with the orifice opening parallel to the pipe wall and to the flow in the pipe. Measurements of the fluid flow in these pipes by the use of this type of pressure sensing element generally relies on the detection of pressure at two different physical locations that have different local flow conditions. The detection of pressure at one location, along with the pressure differential between the two locations, is sufficient to determine the mass flow, if the fluid temperature, standard properties and local flow conditions at the two locations are known. Measured relationships adjusted by empirical correction coefficients are used to express the flow in terms of the two pressures. The mass flow is, to a first approximation, proportional to the square root of the pressure differential. These prior art sensors do not provide information concerning flow direction and also measure static pressure in an area where wall turbulence can cause inaccuracies in the measurements. Other prior art devices include two orifices one of which faces into the flowing fluid and the other faces away from the flowing fluid. Examples of such devices can be found in U.S. Pat. Nos. 3,355,946 and 4,715,232 and Japanese Pat. application Kokai No. 56-148062. Of these devices none are designed to maximize the pressure differential between the orifices or to minimize any flow disturbance created by the device.